340 ballance

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jivemother33

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how can u tell if a 340 is internally or externally ballanced my torque converter is neutrual ballanced with the (i believe it is stock flexplate) ..how can u find the year of ur motor this is the casting # 2780930-340-7 all i can find is it 68-73
 
Your 340 crank shaft can be ID if its a forged or cast crank by the vibration dampener.The biggest item to look for on the VD is a off set weight on the front of the VD.If its there,its a cast crank,if its not its a forged crank.Cast cranks are externally balanced,forged,internally balanced,and the VD is fully round with no external off set weight that you can see.The ID numbers to ID your motor are on the front of the drivers bank,just under where the head and block meet,scratch the paint off or buff the area and you will see it,then I can tell you the who,what and where of your motor.Depending on the year,you can have either crank,mrmopartech
 
look behind the right engine mount. the casting date of your block can be found there. best wat to tell if its internaly or externaly is by the vibration dampener as already stated. IMO external balance is just stupid! i NEVER will rebuild a 340 with an external balanced crank (unless its a # match resto). i will use either the forged 340 crank or a 318 cast crank. either is internaly balanced and have the same demenshons, however the 318 crank is about 3 lbs lighter. in some racing applications 3lbs of rotating weight is huge.
 
chrisII said:
look behind the right engine mount. the casting date of your block can be found there. best wat to tell if its internaly or externaly is by the vibration dampener as already stated. IMO external balance is just stupid! i NEVER will rebuild a 340 with an external balanced crank (unless its a # match resto). i will use either the forged 340 crank or a 318 cast crank. either is internaly balanced and have the same demenshons, however the 318 crank is about 3 lbs lighter. in some racing applications 3lbs of rotating weight is huge.
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The bigger pistons and rods is why you can't just use a 318 cast crank to make it internal balance. As you stated the 318 crank is lighter so it matches the lighter pistons and rods. If it was as easy as putting a 318 cast crank in to make it internal then Mopar would have done it. A 340 cast crank and balancer are special and can't be swapped for other cast cranks or balancers unless some balancing work is done. I have a '73 340 that I put a '65 poly 318 crank in and it required some metal to be added to the counterweights because the poly 318 pistons and rods are lighter than the 340 stuff. I even used the lighter SIR rods and still had to add metal.

Chuck
 
Please correct me if Im wrong but I believe that 72 still had a forged crank,my engine is a 9 of 72 casting and has a forged crank where as my brothers 73 challenger is a cast crank.I guess maybe it depends on if it was installed in a 73 model?.
 
Your engine decodes as this:

E=1969
W=Windsor plant
340=engine displacement
P= secondary code for plant information
261=this should be a 4 digit code for the build sequence for that day
162=is the build date.Double check the dates and post back as a example is:10 16 /october 16 1968,7 11=july 11 1969

Mrmopartech
 
340mopar said:
The bigger pistons and rods is why you can't just use a 318 cast crank to make it internal balance. As you stated the 318 crank is lighter so it matches the lighter pistons and rods. If it was as easy as putting a 318 cast crank in to make it internal then Mopar would have done it. A 340 cast crank and balancer are special and can't be swapped for other cast cranks or balancers unless some balancing work is done. I have a '73 340 that I put a '65 poly 318 crank in and it required some metal to be added to the counterweights because the poly 318 pistons and rods are lighter than the 340 stuff. I even used the lighter SIR rods and still had to add metal.

Chuck
Click to expand...

you are correct that the balance is different, however i have installed a 71 318 cast crank and rods in a 340, with HEAVY trw forged pistons in a low buck 340 circle track motor and it has survived over 1500 laps turning 6000 -6300 rpm twice a lap. I checked a rod bearing after about 600 laps when i brloke a valve and had to replace a piston it still looked great..so i just stuck the piston on the old rod an stuck it together with a different set of heads.
I would not suggest this for an engine you worry about, but when i did it it was either that or not race..as for your early 318 crank in a 340, im confused about this beacuase i always thought the 318 forged crank was the same as a 340 forged.
 
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